This invention relates generally to an electroluminescent lamp and more specifically relates to a multilayered electroluminescent lamp having electric field responsive phosphors contained between the two electrodes.
Electroluminescent lamps are generally fabricated by dispersing electric field responsive phosphors in a high dielectric material, which is disposed between a pair of spaced apart electrically conductive surfaces or electrodes. The application of a suitable electrical voltage between the electrodes builds up an electrical field therebetween, creating a capacitive effect in the dielectric layers to activate the electric field responsive phosphors into luminescence.
Electroluminescent lamps having a single dielectric layer between the electrodes, and such single layer containing phosphors embedded therein, have been in extensive use. The problem frequently encountered, which appreciably affected the brightness of the lamp was the dielectric break down or electrical field leakage due to the microscopic voids or pin holes existing or developing in the layer. To overcome this, a second layer or film of dielectric material, such as a non-vitreous low temperature cure plastic dielectric, was applied over the phosphor dielectric layer to plug up the voids. Although the fusing temperature for the second dielectric layer was less than the fusing temperature for the phosphor-dielectric, the phosphor-dielectric layer was subjected to a second heat treatment, which could have an undesirable effect on the illuminating phosphors.
The present invention minimizes the heating of the phosphor-dielectric layer and provides additional dielectric layers to maintain a high dielectric barrier between the electrodes and also to enhance the illuminating quality of the phosphors.
Previous to the subject invention the dielectric layers for the electroluminescent lamps were heated to the fusion temperature and thereafter cooled for fusing one layer with a contiguous layer. During the fusing process, the adjoining layers would distort or warp with respect to each other. The distortion was not sufficiently reduced even when the coeficient of expansion was substantially the same for the adjoining layers. The effect of such distortion was to reduce the overall brightness of the lamp or diminish the light intensity at various points along the lamp and decrease the useful life of the lamp. In the invention herein, as will be more fully described below, the distortion is virtually eliminated by heating the dielectric layers at three distinct temperature levels--a preheat level, a fusion heat level, and a cooling/heat level.
Accordingly, the primary object of the invention is to provide an electroluminescent lamp having substantial brightness from the phosphor particles embedded therein which respond to the electrical field built up between two electrodes. A related object is to provide optimum brightness and long life for the electroluminescent lamp.
Another object is to provide a method for forming a multilayered electroluminescent device which minimizes the distortion or warping between the contiguous surfaces of the layers.